A Uranium(II) Arene Complex That Acts as a Uranium(I) Synthon

Abstract

Two-electron reduction of the amidate-supported U(III) mono(arene) complex U(TDA) 3 (2) with KC 8 yields the anionic bis(areneEPR spectroscopy, magnetic susceptibility measurements, and calculations using DFT as well as multireference CASSCF methods all provide strong evidence that the electronic structure of 3 is best represented as a 5f 4 U(II) metal center bound to a monoreduced arene ligand. Reactivity studies show 3 reacts as a U(I) synthon by behaving as a twoelectron reductant toward I 2 to form the dinuclear U(III)−U(III) triiodide species 6) and as a three-electron reductant toward cycloheptatriene (CHT) to form the U(IV) complex [K[2.2.2]cryptand][U(η 7 -C 7 H 7 )(TDA) 2 (THF)] ( 7). The reaction of 3 with cyclooctatetraene (COT) generates a mixture of the U(III) anion [K[2.2.2]cryptand][U(TDA) 4 ] (1-crypt) and U(COT) 2 , while the addition of COT to complex 2 instead yields the dinuclear U(IV)−U(IV) inverse sandwich complex [U(TDA) 3 ] 2 (μ-η 8 :η 3 -C 8 H 8 ) (8). Two-electron reduction of the homoleptic Th(IV) amidate complex Th(TDA) 4 (4) with KC 8 gives the mono(arene) complex [K[2.2.2]cryptand][Th-(TDA) 3 (THF)] (5). The C−C bond lengths and torsion angles in the bound arene of 5 suggest a direduced arene bound to a Th(IV) metal center; this conclusion is supported by DFT calculations.

Synthesis, Structure, and Reactivity of the Uranium Bipyridyl Complex [{η5-1,2,4-(Me3Si)3C5H2}2U(bipy)]

“…A more sophisticated approach represents the synthesis of well-defined compounds which react in the presence of suitable substrates as a surrogate for An­(II) . Instrumental to the latter strategy have been redox-active ligands such as 2,2′-bipyridine, 1,4-diazabutadiene, pyridine diimine, and arenes, which store and supply electrons when needed. Early examples for such species were provided by Gambarotta and co-workers, who employed naphthalene as a redox-active ligand unit and prepared some well-characterized thorium arene compounds serving as a source for divalent thorium­(II). , In contrast, in our studies, we employed diimine ligands such as 2,2′-bipyridine (bipy) and synthesized well-behaved bipy actinide metallocenes, [{η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 } 2 An­(bipy)] (An = Th, U), [(η 5 -C 5 Me 5 ) 2 An­(bipy)] (An = Th, U), [{η 5 -1,3-(Me 3 C) 2 C 5 H 3 } 2 Th­(bipy)], and [{η 5 -1,3-(Me 3 Si) 2 C 5 H 3 } 2 U­(bipy)] .…”

Synthesis and Reduction of Heteroleptic Bis(cyclopentadienyl) Uranium(III) Complexes

“…The U­(II) ion with a 5f 3 6d 1 electron configuration has also been found not only in tris­(cyclopentadienyl) coordination environments but also in [K­(crypt)]­[U­(NR 2 ) 3 ] (R = SiMe 3 ) and (C 5 i Pr 5 ) 2 U . However, the U­(II) complexes [K­(crypt)­{[( Ad,Me ArO) 3 mes]­U}, (NHAr iPr6 ) 2 U, and [K­(crypt)]­{U­[ N -(2,6-di-isopropylphenyl)­pivalamido] 2 } have been found to contain 5f 4 ions.…”

Small-Molecule Activation Mediated by [η5-1,3-(Me3Si)2C5H3]2U(bipy)

“…A possible solution to this problem represents well-defined complexes that mimic the reactivity of An­(II) species . Within this approach, redox-active ligands such as 2,2′-bipyridine (bipy), 1,4-diazabutadiene, pyridine diimine, and arenes are installed at the actinide atom, and these ligands can then either store or deliver electron to the actinide atom when necessary and thereby obliviate the necessity of An­(II) intermediates. For example, the group of Gambarotta prepared well-defined thorium arene compounds, which serve as a source of divalent thorium­(II). , As part of our studies, we have relied on redox-active diimine ligands such as 2,2′-bipyridine (bipy) to achieve this goal and prepared well-behaved bipy actinide metallocenes, [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 An­(bipy) (An = Th, U), (η 5 -C 5 Me 5 ) 2 An­(bipy) (An = Th, U), and [η 5 -1,3-(Me 3 C) 2 C 5 H 3 ] 2 Th­(bipy) .…”